Rig Changing Poses By Itself
Nevermind, I fixed it. So, even though I was applying each keyframe with "whole character" I only ever had one bone selected while doing so. I tried doing the same thing with the entire rig selected and it didn't mess up. I'm not really sure what the correlation is between my issue and applying keyframes like that, or why I didn't need to do it that way for all my other animations, but what's fixed is fixed.